IIRC the original version of the “score exchange” site (with a different name - SibeliusMusic?) was Sibelius-only, and run by the Sibelius company. There was also a (non-technical) music discussion forum associated with it.
Eventually they both more or less died through lack of software maintenance. For example the original site used Sibelius Scorch for score display, but that became unsupported in some web browsers, and has now been superseded by Avid’s cloud-based file sharing software.
The original creators of the web site launched the current, independent, site and came to some arrangement with Avid to do a bulk import of scores and user profiles, etc, for the users who gave permission.
So if there are any technical or contractual issues with publishing Dorico scores on scoreexchange.com, I think you need to take them up with the scoreexchange admin.